1. Field of the Invention The present invention is in the field of incandescent light bulbs and in particularly relates to a structure for a flashlight bulb.
2. The Prior Art
In one well-known technique for constructing flashlight bulbs, a pressed and sintered glass bead is used. The bead typically is cylindrical in shape and two holes extend through it in the axial direction. Wires are inserted into these holes, and fused to the bead. The wires extend in the axial direction on both sides of the bead. A filament is then welded to the ends of the wires. This intermediate structure is then placed in a fixture and a cylindrical glass envelope that is closed at one end is placed over the filament so that the rim of the open end of the glass envelope rests against the bead. At this stage, the structure is placed in a vacuum chamber and heat is applied to bond the glass envelope to the glass bead.
The applied heat causes the glass envelope to soften and to seal against the bead. Because the glass envelope is softened and because it must collapse against the bead in order to form a seal, it is not uncommon for the cylindrical envelope to assume a position that is not parallel to the direction of the wires and not parallel to the axis of the cylindrical bead. As a result, the filament is not centered within the envelope, and does not lie on the axis of the bulb.
This displacement of the filament from its correct position is very undesirable, particularly in applications where the reflector (or other apparatus used with the flashlight bulb) positions the flashlight bulb with respect to the reflector. The filament will then be off axis with respect to the reflector. This has the undesirable result that the flashlight beam will not be parallel to the axis of the flashlight. In addition, because the filament is not located on the axis of the reflector, certain optical aberrations that are inherent in the reflector are greatly aggravated. The beam that is produced does not form as small a spot, and the difference in illumination can very well be three to one with a filament that is centered versus a non-centered filament. In short, the lateral displacement of the filament from its correct position with respect to the reflector has serious consequences for the ability of the flashlight to form a small, bright spot that is located on the axis of the flashlight, where the user expects it to be.
The present invention relates to a flashlight bulb structure that results in the filament being located on the axis of the reflector, and accordingly solves the problems associated with the flashlight bulbs of the prior art.